The invention relates to an apparatus and method for slitting underground conduits, and in particular to slitting flexible underground pipes formed from plastics, thermoplastics, rubbers and ductile metals.
A variety of systems are known for splitting rigid underground pipe made from concrete or cast iron. Typically, such methods make use of a slitting wedge or knife that is drawn through the pipe with a cable or chain attached to a winch or a piece of mobile equipment. In the case of pipe formed from relatively brittle materials such as concrete or cast iron, an impact hammer is attached to the wedge to aid in splitting and/or bursting the pipe. In some instances, new pipe is attached to the splitting tool and simultaneously pulled through the bore as the old pipe is burst or slit.
In one widely practiced method, a pneumatic impact boring tool such as a xe2x80x9cHammerhead Molexe2x80x9d (a registered trademark of Earth Tool Co.) boring tool is sent through the existing pipeline such that the head of the tool, which may be provided with blades that apply intense local pressure to the existing pipe, fractures or splits the existing pipe. See Streatfield et. al., U.S. Pat. Nos. 4,720,211, 4,738,565 and 4,505,302. A replacement pipe, typically made of plastic such as HDPE (High Density Polyethylene), can be drawn along behind the boring tool. Pneumatic impact boring tools are well known and are, for example, described in Wentworth et al. U.S. Pat. Nos. 5,025,868 or 5,337,837. The Streatfield et al. process has proven effective commercially because it bursts the old pipe into a multitude of fragments and replaces it with a new pipe at the same time. However, the Streatfield et al. method is less effective on ductile or non-frangible pipes such as copper, lead and certain types of plastic, such as HDPE.
One method for replacing existing underground pipelines is described in U.S. Pat. No. 6,171,026, issued to Crane et al. and assigned to Earth Tool Company, L.L.C., of Oconomowoc, Wis., the disclosure of which is incorporated herein by reference for all purposes. Briefly, the method includes creating open access to opposite ends of an existing pipeline to form an entry opening and an exit opening and mounting a wedge on a cable. The cable is threaded through the existing pipeline and the wedge is positioned at one of the ends of the existing pipeline after which the wedge is pulled through the pipeline from the other end of the existing pipeline so that the wedge slits the existing pipeline to form a slit pipe in the borehole. After the slit pipe is removed from the borehole, a replacement pipeline is pulled into the borehole.
The above described methods have not however, proven satisfactory in all cases. In some cases the methods have been ineffective in splitting underground conduits formed from relatively flexible materials such as high density polyethylene. This is especially in the case of relatively small diameter pipes, on the order of from one-half inch to about eight inches in diameter. The invention described below provides a means of alleviating and overcoming the difficulties encountered in splitting relatively small diameter underground pipes and conduits.
The invention provides method of slitting a flexible conduit in an underground bore, the conduit having entry and exit ends thereof exposed for access, including (1) fitting a retainer to flexible underground conduit adjacent to the entry end thereof, the retainer securing the flexible conduit to limit longitudinal movement thereof relative to the bore, (2) passing pulling means through the flexible conduit, (4) connecting the pulling means to a pipe slitter, and pulling the pipe slitter through the retainer and flexible conduit to slit the conduit, the retainer holding the flexible conduit taut as the slitter passes through the conduit. A slitter nose guide may be positioned on the pulling means ahead of the slitter to aid in maintaining the alignment of slitter in the pipe during the slitting operation.
In one aspect of the method, the retainer comprises a shoring clamp assemble adapted to be secured to the end of the flexible conduit and the method includes securing the clamp assembly onto the conduit. In this aspect the method may be implemented by splitting the entry end of the pipe with a saw or similar tool after which the shoring clamp is clamped onto a split end of the pipe. The clamp assembly may comprise a two piece assembly, such as a pair of ring clamps wherein at least one split end of the flexible conduit is positioned between the pieces which are clamped onto the split end by bolting or screwing the clamps together. An expander may be used with the slitter to expand the bore, and in some cases multiple passes through the bore may be made with larger expanders to further increase the size of the borehole. A replacement pipe may also be attached to the slitter, in which case the replacement pipe is pulled behind the slitter through the retainer and the bore in a single pass application of the method.
In yet another aspect of the invention, an apparatus for slitting a flexible conduit in an underground bore includes a pipe slitter and retaining means adapted to be fastened to an entry end of the flexible conduit. The retaining means includes an opening therethrough for passage of the pipe slitter therethrough and into the conduit and serves to limit longitudinal movement of the conduit relative to the bore as the pipe slitter is pulled through the conduit. A pulling apparatus such as a winch or a piece of mobile equipment is positioned adjacent to an exit opening of the conduit to pull the slitter through the conduit. A flexible pulling means for connecting the slitter to the pulling apparatus through the conduit may comprise a cable, rope, chain or rod.
In this aspect, the retaining means is preferably a pair of ring clamps adapted to be secured on the end of the pipe, although clamps have other geometries that may be used. The ring clamps are adapted to clamp a split end of the conduit between them to limit longitudinal movement of the flexible collar by transferring longitudinal forces applied to the flexible conduit to a wall of a pit adjacent to the entry end of the flexible conduit. The clamps are configured with a central opening that is large enough to accommodate the slitter, allowing it to pass through the opening into the pipe to be slit. The slitter may also include an expander and/or adapter for attaching a replacement pipe if the replacement pipe is to be pulled behind the slitter through the bore. Additionally, the slitter may be provided with a hollow, cylindrical nose guide for maintaining the alignment of the slitter in the flexible conduit during the slitting operation.